Increased platelet inhibition after switching from maintenance clopidogrel to prasugrel in patients with acute coronary syndromes: Results of the SWAP (SWitching Anti Platelet) study

Objectives The objective was to evaluate the pharmacodynamic response of switching patients on maintenance phase clopidogrel therapy after an acute coronary syndrome (ACS) to prasugrel. Background Prasugrel P2Y₁₂ receptor blockade is associated with greater pharmacodynamic platelet inhibition and reduction of ischemic complications compared with that of clopidogrel in ACS patients undergoing percutaneous coronary intervention. The pharmacodynamic effects of switching patients during maintenance phase clopidogrel therapy after an ACS event to prasugrel are unknown. Methods The SWAP (SWitching Anti Platelet) study was a phase 2, multicenter, randomized, double-blind, double-dummy, active-control trial. After a run-in of daily open-label clopidogrel 75 mg with aspirin therapy for 10 to 14 days, patients were randomly assigned to 1 of the following 3 treatments: placebo loading dose (LD)/clopidogrel 75 mg maintenance dose (MD), placebo LD/prasugrel 10 mg MD, or prasugrel 60 mg LD/10 mg MD. Platelet function was evaluated at 2 h, 24 h, 7 days, and 14 days using light transmittance aggregometry, VerifyNow P2Y ₁₂ assay, and vasodilator-stimulated phosphoprotein phosphorylation. Results A total of 139 patients were randomized, of whom 100 were eligible for analysis. Maximum adenosine diphosphate-induced platelet aggregation (20 μM) by light transmittance aggregometry at 1 week (primary end point) was lower after prasugrel MD compared with clopidogrel MD (41.1% vs. 55.0%, p < 0.0001), and was also lower in the prasugrel LD+MD group compared with clopidogrel MD (41.0% vs. 55.0%, p < 0.0001). At 2 h, a prasugrel LD resulted in higher platelet inhibition compared with the other regimens. Similar results were found using light transmittance aggregometry with 5 μM adenosine diphosphate, VerifyNow P2Y₁₂, and vasodilator-stimulated phosphoprotein phosphorylation assays. Conclusions For patients receiving maintenance clopidogrel therapy after an ACS event, switching from clopidogrel to prasugrel is associated with a further reduction in platelet function by 1 week using prasugrel MD or within 2 h with the administration of a prasugrel LD. (A Pharmacodynamic Comparison of Prasugrel [LY640315] Versus Clopidogrel in Subjects With Acute Coronary Syndrome Who Are Receiving Clopidogrel [SWAP]; NCT00356135)